In a railroad vehicle, an air spring is disposed between a bodywork and a truck in order to alleviate impacts and vibrations imposed on the bodywork in travelling. The air spring generally includes a top plate connected to the bodywork, a bottom plate disposed on the truck, and a rubber diaphragm disposed to connect the top plate and the bottom plate to each other. The diaphragm can alleviate impacts and vibrations while the vehicle is travelling through elastic deformation. As a constituent material for members such as the top plate and the bottom plate, from the viewpoint of ensuring abrasion resistance and strength thereof, metal such as aluminum or iron is commonly adopted (for example, see Japanese Patent Laying-Open No. 2009-138905 (PTD 1)).